Delete update notification?

Shortly, I received a notification about a system update on my Z2 tablet.
I decided, not to update my device to the latest version as long as I don't know what changes will be done with this update and there is also no change history to be found...
Unfortunately, I now have a symbol for that update in the notification bar and can't get rid of it.
Does anybody know, how to remove the notification/symbol without updating?
Thanks!

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